Process for hydroxylation of aromatic compounds, hydroxylation catalyst and process for preparing same

ABSTRACT

The present invention relates to a process for hydroxylation of a compound of formula (I) by reacting the compound of formula (I) with an oxidizing agent, in the presence of a titanium silicalite zeolite prepared by crystallization preceded by a maturing step. The present invention also relates to a titanium silicalite zeolite and to the process for preparing same.

The hydroxylation of aromatic compounds, such as phenols, in thepresence of an oxidizing agent, especially aqueous hydrogen peroxidesolution, and of a catalyst leads to the formation of hydroxylatedaromatic compounds, such as hydroquinone (HQ) and pyrocatechol (PC) forphenol, but also to the formation of side products, especially tars. Tolimit the formation of these tars, the conversion of the startingaromatic compound should be limited, and is, for example, in the case ofphenol, from 5% to 30%. More specifically, the demand for hydroquinoneis relatively high, especially in the field of polymerizationinhibitors. One way of satisfying this increasing demand forhydroquinone would be to orient the hydroxylation reaction of phenoltoward the formation of hydroquinone.

The prior art, especially FR 2 071 464 discloses the use of ahomogeneous catalyst of optionally modified strong acid type, for thehydroxylation of phenol. The use of this hydroxylation reaction ofphenol in the presence of a homogeneous strong acid catalyst leads tothe formation of hydroquinone and pyrocatechol in a PC/HQ mole ratio,depending on the acid used, of greater than or equal to 1.5. In general,the use of a homogeneous catalyst leads to the formation of hydroquinoneand pyrocatechol in a PC/HQ mole ratio of greater than or equal to 1.

It is also known from the prior art, especially from FR 2 523 575, touse a zeolite of titano-silicalite type of structure MFI or MEL,especially TS-1 or TS-2, respectively, a heterogeneous catalyst, for thehydroxylation of phenol. It is thus possible to obtain hydroquinone andpyrocatechol with a PC/HQ mole ratio of less than 1.3, especiallybetween 0.4 and 1.3, depending on the catalyst or the solvent used inthe phenol hydroxylation reaction.

It is, however, worthwhile providing a process for obtaining the lowestpossible PC/HQ mole ratio in order to promote the formation ofhydroquinone while at the same time maintaining the highest possibleyield in an environmentally friendly solvent such as water.

TS-1 and TS-2 are zeolites characterized by the presence of titaniumatoms in replacement for silicon atoms in the structure. These zeoliteshave, respectively, a structure MFI or MEL and are generally obtained bymixing a source of silicon, a source of titanium, a structuring agentand a mineralizing agent, the mixture obtained then being crystallizedfor 1 to 10 days at a temperature typically close to 175° C. and finallycalcined for 3 to 12 hours, at a temperature typically close to 550° C.Processes for preparing TS-1 are especially described in U.S. Pat. No. 4410 501 or EP 0 311 983.

TS-1 and TS-2 have advantageous catalytic properties and are thus usedin many reactions such as the hydroxylation of phenol, the ammoximationof cyclohexanone or the epoxidation of alkenes.

Many studies have been conducted aimed at improving the catalyticperformance of titano-silicalite zeolites. These studies have relatedespecially to the crystallization time, the source of silicon, thesource of structuring agent, the TPAOH/Si mole ratio, the H₂O/Si moleratio or the Ti/(Ti+Si) mole ratio (Van Der Pol et al., Appl. Catal. AGeneral, 1992 92 93-111).

An optimized process should be found for preparing titanium silicalitessuch as TS-1 or TS-2, making it possible to improve their catalyticproperties, especially in the context of the hydroxylation reaction ofaromatic compounds, and in particular of phenol.

One object of the present invention is to provide an improved processfor the hydroxylation of aromatic compounds, and in particular ofphenol, anisole and para-t-butylphenol.

Another object of the present invention is to provide a process for thehydroxylation of phenol which allows the preparation of hydroquinone andpyrocatechol with a PC/HQ mole ratio of less than 1.4, preferably lessthan 1.2, more preferably less than 1, preferably strictly less than 0.8and preferably strictly less than 0.7.

Another object of the present invention is to provide atitano-silicalite zeolite that is suitable for use in this process forthe hydroxylation of aromatic compounds.

Other objects will become apparent on reading the description of theinvention that follows.

The present invention relates to a process for the hydroxylation of acompound of formula (I):

in said formula:

-   n is a number from 0 to 4 and preferably equal to 0, 1, or 2,-   R₁ represents a hydrogen atom or an alkyl, cycloalkyl, aryl or    aralkyl group,-   R₂, which may be identical or different, represent an alkyl, alkoxy    or hydroxyl group, a halogen atom or a perhaloalkyl group;    by reaction of the compound of formula (I) with an oxidizing agent,    in the presence of a titano-silicalite zeolite prepared by    crystallization, preceded by a maturation step.-   In the context of the invention, the term “alkyl” means a linear or    branched C₁-C₁₅, preferably C₁-C₁₀ and even more preferentially    C₁-C₄ hydrocarbon-based chain. Examples of preferred alkyl groups    are especially methyl, ethyl, propyl, isopropyl, butyl, isobutyl and    t-butyl.-   The term “alkoxy” means a group alkyl-O— in which the term “alkyl”    has the meaning given above. Preferred examples of alkoxy groups are    methoxy or ethoxy groups.-   The term “cycloalkyl” means a C₃-C₈ monocyclic, cyclic    hydrocarbon-based group, preferably a cyclopentyl or cyclohexyl    group or a C₄-C₁₈ polycyclic (bicyclic or tricyclic) group,    especially adamantyl or norbornyl.-   The term “aryl” means a monocyclic or polycyclic aromatic,    preferably C₆-C₂₀ monocyclic or bicyclic group, preferably phenyl or    naphthyl. When the group is polycyclic, i.e. when it comprises more    than one cyclic nucleus, the cyclic nuclei may be fused in pairs or    attached in pairs via σ bonds. Examples of (C₆-C₁₈)aryl groups are    especially phenyl and naphthyl.-   The term “aralkyl” means a linear or branched hydrocarbon-based    group bearing a C₇-C₁₂ monocyclic aromatic ring, preferably benzyl:    the aliphatic chain comprising 1 or 2 carbon atoms.-   The term “perhaloalkyl group” means an alkyl group comprising from 1    to 10 carbon atoms and from 3 to 21 halogen atoms, preferably    fluorine, and more particularly the trifluoromethyl group.-   In formula (I), the term “halogen atom” preferably defines fluorine,    chlorine and bromine.-   The substrates to which the process of the invention applies are    especially phenol; aliphatic phenol ethers; monoalkylphenols,    dialkylphenols, trialkylphenols with C₁-C₄ alkyl groups;    alkoxyphenols with C₁-C₄ alkoxy groups.-   Among the substrates of formula (I) that may be used in the process    of the invention, mention may be made in a nonlimiting manner of    phenol; aliphatic phenol ethers such as anisole or phenetole;    alkylphenols such as o-cresol, p-cresol, m-cresol,    4-tert-butylphenol (or para-tert-butylphenol); alkoxyphenols such as    2-methoxyphenol (guaiacol), 4-methoxyphenol or 2-ethoxyphenol    (guetol).

Preferably, in the compound of formula (I), R₁ is a hydrogen atom, amethyl group or an ethyl group, and more preferably R1 is hydrogen. Evenmore preferably, n=0 in the compound of formula (I). Veryadvantageously, in the compound of formula (I), n=0 and R₁ is a hydrogenatom, a methyl group or an ethyl group. In a particularly preferredmanner, the compound of formula (I) is phenol or anisole.

In another embodiment and advantageously, in the compound of formula(I), R₁ represents H, R₂ represents a tert-butyl and n=1, R₂ preferablybeing in the para position.

The hydroxylation process according to the invention makes it possibleespecially, Starting with phenol, to prepare hydroquinone andpyrocatechol with a PC/HQ mole ratio of less than 1.4, preferably lessthan 1.2, more preferably less than 1, preferably strictly less than 0.8and more preferably strictly less than 0.7. Advantageously, the PC/HQmole ratio is at least equal to 0.05.

Preferably, the oxidizing agent is hydrogen peroxide (H₂O₂). Preferably,the oxidizing agent is used in a mole ratio relative to the compound offormula (I) of from 0.005 to 0.60, preferably from 0.05 to 0.50 and evenmore preferably from 0.15 to 0.35. The hydrogen peroxide titer istypically from 10% to 70% and usually from 20% to 30%.

Preferably, the hydroxylation reaction is performed in the presence of asolvent, chosen especially from protic solvents and aprotic solvents, ora mixture of these solvents. The process may especially be performed inwater, in a erotic solvent, in an aprotic solvent or in a water/proticsolvent or water/aprotic solvent mixture. The protic solvent may bechosen from water, alcohols, especially methanol, ethanol, propanol,isopropanol or tert-butanol, and acids, especially acetic acid. Thehydroxylation reaction is particularly preferably performed in water.The aprotic solvent may be acetone and any other ketone, nitriles suchas acetonitrile, or esters such as methyl acetate, ethyl acetate, propylacetate or butyl acetate.

Preferably, the solvent is used in a mole proportion of from 0.05 to 50and preferably from 0.2 to 20, relative to compound (I).

According to one variant, as specified above, the water may be mixedwith other solvents in water/solvent mole proportions of from 1/0.01 to1/20 and preferably from 1/0.1 to 1/2.

In a particular embodiment, the process according to the invention is aprocess for the hydroxylation of phenol leading to the formation ofpyrocatechol and hydroquinone. In a particularly advantageous manner,the process of the invention makes it possible to obtain hydroquinoneand pyrocatechol in a PC/HQ mole ratio of less than 1.4, preferably lessthan 1.2, more preferably less than 1, even more preferably strictlyless than 0.8 and more preferably strictly less than 0.7.

In another particular embodiment, the process according to the inventionis a process for the hydroxylation of anisole.

In another particular embodiment, the process according to the inventionis a process for the hydroxylation of para-tert-butylphenol.

The process of the invention may especially be performed at atemperature of from 50° C. to 120° C. and preferably from 70° C. to 100°C. The process of the invention may especially be performed for a periodof from 5 minutes to several days, for example from 5 minutes to 100hours.

The process according to the invention is advantageously performed in areactor functioning in batch mode, in semi-batch mode or in continuousmode. Various types of reactor may be used for performing the processaccording to the invention. Advantageously, the process according to theinvention is performed in a stirred reactor or a cascade of stirredreactors or alternatively in a piston-flow reactor, for example atubular reactor placed horizontally, vertically or inclined.

The process according to the invention is preferably performed with amass ratio of zeolite relative to the compound of formula (I) of from0.001 to 0.30, preferably from 0.01 to 0.10 and even more preferablyfrom 0.01 to 0.06.

Preferably, the matured titano-silicalite zeolite used for performingthe hydroxylation process according to the invention is a zeolite TS-1or TS-2, respectively, from the MFI family or from the MEL family. Suchzeolites are described in the prior art, but are modified according tothe invention by the introduction of a maturation step beforecrystallization to be used for performing the hydroxylation processaccording to the invention.

The present invention thus relates to a matured titano-silicalitezeolite, preferably matured TS-1 or TS-2, preferably TS-1, characterizedby an apparent mean particle size of from 10 to 300 nm, preferably from20 to 150 nm and more preferably from 35 to 75 nm. The mean apparentsize of the crystallites was calculated, according to the Scherrerformula, from the mid-height width of x-ray diffraction lines. It waschosen to work with the line (101) (2θ=7.9°) (FIG. 1). The structuralstudy of the various materials is performed using an X PERT Prodiffractometer. The diffractograms are recorded over a 2θ angular rangefrom 5° to 90° at 200 seconds per 0.02° step. The size of thecrystallites was also determined by means of an Ultra 55 Zeiss fieldeffect scanning electron microscope (SEM/FEG) equipped with an InLensdetector (FIG. 2) and a Jeol 2010F transmission electron microscopeequipped with a field emission cannon functioning at 200 kV (FIG. 3).The size distribution of the crystallites was also determined by dynamiclight scattering (DLS). The measurements were taken at 20° C. using aVasco DL135 granulometer from the company Cordouan Technologies. Thesize distribution of the crystallites was calculated from theautocorrelation function using the Padé-Laplace algorithm (FIG. 4). Themeasurements were applied to synthetic solutions (i.e. to the solutionsobtained after maturation, after crystallization and before calcinationof the materials) diluted from 10 to 400 times in demineralized waterand/or treated with ultrasound for 1 to 10 minutes, but also tosolutions obtained after dispersion of 50 to 100 mg of calcined catalystin 10 g of demineralized water, and treated with ultrasound for 15minutes.

Preferably, this zeolite is also characterized by an infrared absorptionband at 550 cm⁻¹ and an infrared absorption band at 960 cm⁻¹ (FIG. 5).The infrared absorption bands at 420 cm⁻¹, 800 cm⁻¹, 1070 cm⁻¹ and 1220cm⁻¹, conventionally obtained for any material based on SiO₂, are alsoobserved. The ratio between the area of the band at 960 cm⁻¹ (A₉₆₀) andthe area of the band at 550 cm⁻¹ (A₅₅₀) ranges between 0 and 1 andpreferably between 0.4 and 0.7. The analyses were performed with a Jasco4200 Fourier transform infrared spectrometer (FT/IR), in attenuatedtotal reflection (ATR), between 400 and 4000 cm⁻¹.

Preferably, this zeolite is also characterized by a UV absorption bandof between 210 and 240 nm (FIG. 6). The presence of titanium oxide (UVabsorption band at about 330-360 nm) may also be demonstrated by thischaracterization technique. The analyses were performed with aPerkin-Elmer Lambda 950 spectrophotometer for wavelengths of between 190and 500 nm.

The matured zeolite according to the invention used in the hydroxylationprocess according to the invention may be advantageously obtained via amanufacturing process comprising a maturation step.

Advantageously, this maturation step makes it possible to obtain azeolite with an outer surface area (measured from the slope of thenitrogen adsorption curve represented according to the t-plot method) offrom 60 m²/g to 300 m²/g and preferably from 60 to 150 m²/g and/or aninter-grain distance (measured according to the Barrett-Joyner-Halendamethod=BJH method) of from 5 to 50 nm and preferably from 10 to 30 nm.Advantageously, the specific surface area of this zeolite (measuredaccording to the Brunauer-Emmett-Teller method=BET method) is between350 and 600 m²/g and preferably between 400 and 500 m²/g. The microporesize is particularly between 0.40 and 0.50 nm and preferably between0.44 and 0.46 nm (measured by the Horvath-Kawazoe method=HK method). Themeasurement of the amount of nitrogen that is able to be adsorbed ontothe surface of a porous solid, as a function of the relative pressureP/P₀, makes it possible to determine the specific surface area, thevolume and the diameter of the pores. The adsorption and desorption ofnitrogen are performed in liquid nitrogen (at −196° C.) using a BelsorpMax machine. The sample is pretreated under a secondary vacuum at 250°C. for 16 hours. The mass of analyzed sample is about 50-100 mg.Nitrogen adsorption and desorption isotherms for a TS-1 are reported asin the example in FIG. 7. The nitrogen adsorption takes place first inthe micropores. Consequently, analysis of the first part of the curve(P/P₀<0.02) makes it possible to determine the volume and size of themicropores (BET method and HK method). Next, once the micropores havebeen filled, adsorption takes place on the outside of the particles.Exploitation of the second part of the curve (0.02<P/P₀<0.85) givesaccess to the outer surface area of the material (measured from thet-plot method). Finally, for relative pressures of greater than 0.85, weobserve hysteresis due to capillary condensation in the mesopores of thematerial. These mesopores are inter-grain pores, derived from cloggingtogether the particles. Analysis of the final part of the curve(P/P₀>0.85) makes it possible to determine the volume and size of themesopores (equivalent to the inter-grain distance) (BJH method).

Preferably, the zeolite has a mole ratio Ti/(Ti+Si) of from 0.0001 to0.10 and preferably from 0.0001 to 0.05, for example from 0.005 to 0.04.

The present invention also relates to a process for preparing atitano-silicalite zeolite, comprising the following steps:

-   -   a) preparation of a zeolite precursor from at least one source        of silicon, at least one source of titanium, at least one        mineralizing agent and at least one structuring agent;    -   b) maturation of the precursor;    -   c) crystallization of the matured precursor, and optionally    -   d) calcination of the matured and crystallized precursor,        especially to obtain the zeolite according to the invention.

Step a) of preparing the precursor may be performed according to anymethod known to those skilled in the art.

In a particular embodiment, step a) is performed according to A. J. H.P. Van Der Pol et al. (Appl. Catal. A General 1992 92 93-111), andespecially comprises the following steps:

-   -   i. mixing the source of titanium and the source of silicon;    -   ii. adding to the solution obtained in i), dropwise, under cold        conditions, preferably at 0° C., an aqueous solution of        structuring agent and of mineralizing agent;    -   iii. heating the solution obtained in ii) to a temperature of        from 60 to 100° C., preferably 80° C.;    -   iv. adding demineralized water.

Preferably, the mixture according to step (i) is stirred for 30 minutesto 2 hours, preferably for 1 hour, at a temperature of from 20 to 50° C.and preferably from 25 to 40° C.

Preferably, step (ii) is performed under an inert atmosphere, forexample under argon.

In another particular embodiment, step a) is performed according to A.Thangaraj et al. (J. Catal. 1991, 130, 1-8), and especially comprisesthe following steps:

-   -   1) mixing a source of silicon and an aqueous solution of        structuring agent and of mineralizing agent;    -   2) mixing a source of titanium and an alcohol, especially        isopropanol;    -   3) adding the solution from step 2) to the solution from step 1)        dropwise at low temperature, preferably 0° C.;    -   4) heating;    -   5) adding demineralized water.

Preferably, the mixing according to step 1) is performed at roomtemperature (20-25° C.) for 0.5 to 5 hours and preferably for 2 to 4hours before step 3).

Preferably, the temperature of step 4) is from 60 to 100° C., forexample 80° C.

In another particular embodiment, step a) is performed according toSerrano et al. (Micro. Mater. 1995, 4, 273-282), and especiallycomprises the following steps:

-   -   A) hydrolysis of a source of silicon with an acidified aqueous        solution, preferably an aqueous HCl solution;    -   B) dissolution of a source of titanium in an alcohol, especially        isopropanol;    -   C) addition of solution B) to solution A);    -   D) addition of an aqueous solution of structuring agent and of        mineralizing agent;    -   E) drying and obtaining a solid material;    -   F) impregnation of the material obtained in step E) with an        aqueous solution of structuring agent and of mineralizing agent        dropwise, and homogenization.

At the end of step D), the material sets to a solid.

Step E) is performed at a temperature of from 60 to 130° C., for exampleat 100° C.; for 6 hours to 5 days, for example for 3 days.

The source of titanium and the source of silicon may be any compoundknown to those skilled in the art that may serve for the preparation oftitano-silicalite zeolite (for example those described by Perego et al.(Applied Catalysis A: General, 2001, 221, 63-72)). Preferably, thesources of titanium and silicon are chosen from titanium or siliconoxides, titanium or silicon alkoxides and titanium or silicon halides.Preferably, the source of titanium is a titanium alkoxide, for exampletetraethoxytitanium (TEOT) or tetrabutoxytitanium (TBOT). Preferably,the source of silicon is a silicon alkoxide, for example tetraethylorthosilicate (TEOS).

According to the invention, the term “structuring agent” means astructure-directing agent which will allow the formation of the zeolite.The term “mineralizing agent” means any chemical species whose role isto catalyze the hydrolysis and polycondensation of the sources oftitanium and silicon. The same species may act as structuring agent andas mineralizing agent. The various structuring agents that may be used,alone or as mixtures, for preparing TS-1 are chosen fromtetrapropylammonium (TPA⁺), tetraethylammonium (TEA⁺),tetrapropylphosphonium (TPP⁺), tetraethylphosphonium (TEP⁺) andhexapropyl-1,6-hexanediammonium (di-TPA⁺), the mineralizing agent thenpossibly being the counterion chosen from HO⁻, F⁻ and amine. The variousstructuring agents that may be used, alone or as mixtures, for preparingTS-2 are chosen from tetrabutylammonium (TBA⁺) and3,5-dimethyl-N,N-diethylpiperidinium (DMDEP⁺), the mineralizing agentthen possibly being the counterion chosen from HO⁻, F⁻ and amine.

Preferably, in the process of the invention, tetrapropylammoniumhydroxide (TPAOH) acts as structuring agent and mineralizing agent (TPA⁺structuring agent and HO⁻ mineralizing agent). The aqueous solution ofstructuring agent is typically an aqueous solution containing between20% and 40% by weight of structuring agent.

Advantageously, the mole ratios of structuring agent/Si and mineralizingagent/Si, and especially the mole ratio TPAOH/Si, are from 0.09 to 0.55and preferably from 0.17 to 0.45.

Advantageously, the H₂O/Si mole ratio is between 4 and 80 and preferablybetween 10 and 30.

In a particularly advantageous manner, step b) of maturation of thetitano-silicalite zeolite corresponds to a step of thermal heating,before crystallization, with or without stirring, at a temperature offrom 20 to 120° C., preferably at a temperature of from 70 to 100° C.and more preferentially 80° C. or 90° C. Preferably, the maturation stepb) is performed for between 30 minutes and 9 months and preferablybetween 1 hour and 15 days. In a particular embodiment, the maturationstep b) corresponds to a step of thermal heating, beforecrystallization, at a temperature of from 20 to 120° C. and preferablyfrom 20 to 110° C., for 30 minutes to 9 months. Preferably, thematuration step is performed between 70 and 100° C. for between 1 hourand 15 days and preferentially at 80° C. for between 10 and 35 hours oralternatively at 90° C. for between 2 and 20 hours. The maturation timewill preferentially be shorter for a higher temperature.

In another embodiment, the step of maturation of the titano-silicalitezeolite corresponds to a step of microwave heating, beforecrystallization, with or without stirring, at a temperature of from 40to 120° C., for 1 to 180 minutes. At a temperature equivalent to athermal heating, microwave heating will make it possible to shorten thematuration time. At a time equivalent to a thermal heating, microwaveheating will make it possible to reduce the maturation temperature.

The crystallization step c) may be performed, with or without stirring,at the autogenous pressure of the system or under a pressure of an inertgas, for example nitrogen, for example at a pressure of from 10 to 120bar and preferably from 20 to 120 bar.

In another embodiment, the crystallization step c) may be performed withor without stirring, by microwave heating at a temperature of from 140to 200° C., for example 175° C., for a time of less than 8 hours andparticularly preferably less than 3 hours, for example from 1 to 60minutes.

The process for preparing the titano-silicalite zeolite may alsocomprise a step of washing the crystalline material of step c). Thisstep may be performed via any method known to those skilled in the artand especially by washing with deionized water. This step may especiallybe performed by dispersing the material obtained in step c) in adeionized water, and this washing step may be repeated several times andpreferably until the pH of the solution after washing is less than 9.

The process for preparing the zeolite may also comprise a step ofrecovering the washed material. This step may be performed via anymethod known to those skilled in the art and especially bycentrifugation, especially by centrifugation at low temperature. Thematerial thus obtained is then dried by any method known to thoseskilled in the art, especially by atomization or simple drying at atemperature of from 70 to 110° C., for 10 to 48 hours.

The process for preparing the zeolite may also comprise a final step ofcalcination, This step may be performed via any method known to thoseskilled in the art, especially by heating at a temperature of from 350to 750° C., for example at 550° C., for 2 to 24 hours.

Preferably, the maturation step b) makes it possible to reduce theduration of the crystallization step a) by thermal heating which shouldusually be more than 1 day at 175° C., without modifying the catalyticperformance of the zeolite. Thus, in a particularly advantageous manner,the crystallization step is performed, with or without stirring, from140 to 200° C., for example at 175° C. for a time of less than 1 day,preferably less than 12 hours and particularly preferably less than 8hours, for example from 3 to 6 hours.

The present invention also relates to a titano-silicalite zeolite thatmay be obtained via the process for preparing the same.

In general, the sizes of the particles obtained after maturation, aftercrystallization and before calcination are equivalent, or evenidentical, to those obtained after maturation, after crystallization andafter calcination.

The present invention will now be described with the aid of nonlimitingillustrative examples.

In the examples, all the percentages are given on a weight basis, unlessotherwise indicated, the temperature is expressed in degrees Celsius,unless otherwise indicated, and the pressure is atmospheric pressure,unless otherwise indicated.

FIG. 1 shows the X-ray diffractogram of a titano-silicalite zeolite ofTS-1 type which has undergone a step of maturation at 80° C. for 14hours, and which has then been crystallized for 5 days at 175° C. InFIG. 1, I represents the scattered intensity and θ represents half ofthe angle between the incident beam and the scattered beam.

FIG. 2 is an SEM image of a titano-silicalite zeolite of TS-1 type whichhas undergone a step of maturation at 80° C. for 14 hours, and which hasthen been crystallized for 5 days at 175° C.

FIG. 3 is a TEM image of a titano-silicalite zeolite of TS-1 type whichhas undergone a step of maturation at 80° C. for 23 hours, and which hasthen been crystallized for 5 days at 175° C.

FIG. 4 shows the population (percentage of the number of particles) as afunction of the diameter D of the particles of a titano-silicalitezeolite of TS-1 type which has undergone a step of maturation at 80° C.for 23 hours, and which has then been crystallized for 5 days at 175° C.

FIG. 5 shows the IR spectrum of a titano-silicalite zeolite of TS-1 typewhich has undergone a step of maturation at 80° C. for 14 hours, andwhich has then been crystallized for 5 days at 175° C. In FIG. 5, Rrepresents the reflectance and σ represents the wavenumber.

FIG. 6 shows the UV spectrum of a titano-silicalite zeolite of TS-1 typewhich has undergone a step of maturation at 80° C. for 14 hours, andwhich has then been crystallized for 5 days at 175° C. In FIG. 6, F(R∞)represents the Kubelka-Munk function for an infinite thickness of powderand A represents the wavelength.

FIG. 7 shows the nitrogen adsorption and desorption isotherms for atitano-silicalite zeolite of TS-1 type which has undergone a step ofmaturation at 80° C. for 14 hours, and which has then been crystallizedfor 5 days at 175° C. In FIG. 7, V represents the specific adsorbedvolume in gas equivalent under standard temperature and pressureconditions (STP) and P/P₀ represents the relative pressure of gasrelative to atmospheric pressure.

FIG. 8 shows the UV spectra of various titano-silicalite zeolites ofTS-1 type matured at 80° C. for 14 hours, and then crystallized at 175°C., for 6 hours, 24 hours or 5 days. In FIG. 8, F(R∞) represents theKubelka-Munk function for an infinite thickness of powder and Arepresents the wavelength.

EXAMPLES

Process A for Preparing a titano-silicalite Zeolite According to theInvention

Preparation of the Precursor 377 mmol of Si(OEt)4 (TEOS) (Sigma Aldrich99.0%) and 8 mmol of Ti(OEt)₄ (TEOT) (Alfa Aesar 99+%) are added to apolypropylene flask flushed with a stream of argon. This first solutionis then stirred for 1 hour at 35° C. Next, a second solution containing132 mmol of (C₃h₇)₄NOH (TPAOH) at 20% by weight in water is prepared bydilution with demineralized water of the 25% commercial solution(Acros). The addition of the TPAOH solution takes place at 0° C.,dropwise. The reaction mixture is then heated at 80° C. for about 3hours. Finally, 37 g of demineralized water are added so that the volumeof the precursor solution is equal to ⅔ of the volume of the autoclavein which the titano-silicalite zeolite is then crystallized. The molarcomposition of the resulting clear solution is:SiO₂/TiO₂/TPAOH/H₂O=1/0.02/0.35/21.

Maturation of the Precursor

The precursor obtained is placed in a 250 mL autoclave and is thenheated without stirring at a given temperature of 80° C. or 90° C.,under the autogenous pressure, for a given time of from 4.5 to 48 hours.

Crystallization

The matured precursor is crystallized, without stirring, at 175° C.,under the autogenous pressure, for 6 hours to 5 days.

Washing, Drying, Calcination

The material obtained after the crystallization step is recovered bycentrifugation for 30 to 45 minutes, at 9° C. and 12 000 rpm, and isthen washed, i.e. dispersed in about 150 to 200 mL of demineralizedwater and left stirring for about 1 hour. The washing operation isrepeated a sufficient number of times (in general three times) such thatthe pH of the final washing water is less than 9. Between each wash, thesolid is recovered by centrifugation for 30 to 45 minutes, at 9° C. and12 000 rpm. Next, the product is dried at 80° C. for about 16 hours andis then calcined at 550° C. in air for 3 hours.

This process A describes the preparation of a titano-silicalite-1 (TS-1)zeolite. The production of a titano-silicalite-2 (TS-2) zeolite ispossible by replacing, during the preparation of the precursor, theTPAOH with TBAOH or any other structuring agent allowing the synthesisof TS-2.

Process B for Preparing a titano-silicalite Zeolite

Preparation of the Precursor

377 mmol of TEOS and 132 mmol of TPAOH at 20% by weight in water areadded to a polypropylene flask flushed with a stream of argon. Thisfirst solution is then stirred for 3 hours at room temperature. A secondsolution is then prepared by diluting 8 mmol of Ti(OC₄H₉)₄ (TROT) (Acros99%) in 218 mmol of isopropanol (Acros 99.5%). The addition of thissecond solution takes place dropwise at 0° C., with continued flushingwith argon. The various alcohols present are then removed by heating thereaction mixture at 80° C. for about 3 hours. Finally, 37 g ofdemineralized water are added so that the volume of the precursorsolution is equal to ⅔ of the volume of the autoclave in which thetitano-silicalite zeolite is then crystallized. The molar composition ofthe resulting clear solution is: SiO₂/TiO₂/TPAOH/H₂O=1/0.02/0.35/21.

Maturation of the Precursor

The precursor obtained is placed in a 250 mL autoclave and is thenheated at 80° C. without stirring, under the autogenous pressure, for agiven time of 14 hours.

Crystallization

The matured precursor is crystallized, without stirring, at 175° C.,under the autogenous pressure, for 5 days.

Washing, Drying, Calcination

The material obtained after the crystallization step is recovered bycentrifugation for 30 to 45 minutes, at 9° C. and 12 000 rpm, and isthen washed, i.e. dispersed in about 150 to 200 mL of demineralizedwater and left stirring for about 1 hour. The washing operation isrepeated a sufficient number of times (in general three times) such thatthe pH of the final washing water is less than 9. Between each wash, thesolid is recovered by centrifugation for 30 to 45 minutes, at 9° C. and12 000 rpm. Next, the product is dried at 80° C. for about 16 hours andis then calcined at 550° C. in air for 3 hours.

Process C for Preparing a titano-silicalite Zeolite

Preparation of the Precursor

211 mmol of TEOS are first hydrolysed with 35.2 mL of an aqueoussolution of HCl at 237 mmol/L, with stirring, at room temperature for 2hours. 4.3 mmol of TBOT pre-dissolved in 1.61 mol of isopropanol areadded to this solution. The mixture obtained is then left stirring for20 minutes. Next, 14 mmol of TPAOH at 25% by weight in water are addeddropwise. A few seconds after the addition of the TPAOH, the SiO₂—TiO₂cogel sets to a solid. This solid is then dried at 100° C. for 3 days.16.7 g of dry cogel are then recovered. This cogel is ground and thenimpregnated with 60 mmol of TPAOH at 20% by weight in water. Thisimpregnation is performed by adding the aqueous solution of TPAOHdropwise to the cogel placed in a polypropylene beaker. The mixture ishomogenized using a spatula. Finally, a relatively fluid paste isobtained, the molar composition of which isSiO₂/TiO₂/TPAOH/H₂O=1/0.02/0.35/13.

Maturation of the Precursor

The precursor obtained is placed in a 250 mL autoclave and is thenheated at 80° C. without stirring, under the autogenous pressure, for agiven time of 14 hours.

Crystallization

The matured precursor is crystallized, without stirring, at 175° C.,under the autogenous pressure, for 5 days.

Washing, Drying, Calcination

The material obtained after the crystallization step is recovered bycentrifugation for 30 to 45 minutes, at 9° C. and 12 000 rpm, and isthen washed, i.e. dispersed in about 150 to 200 mL of demineralizedwater and left stirring for about 1 hour. The washing operation isrepeated a sufficient number of times (in general three times) such thatthe pH of the final washing water is less than 9. Between each wash, thesolid is recovered by centrifugation for 30 to 45 minutes, at 9° C. and12 000 rpm. Next, the product is dried at 80° C. for about 16 hours andis then calcined at 550° C. in air for 3 hours.

Process D for Preparing a titano-silicalite Zeolite According to theInvention

Preparation of the Precursor

377 mmol of TEOS and 132 mmol of TPAOH at 20% by weight in water areadded to a polypropylene flask flushed with a stream of argon. Thisfirst solution is then stirred for 3 hours at room temperature. A secondsolution is then prepared by diluting 8 mmol of Ti(OC₄H₉)₄ (TBOT) (Acros99%) in 218 mmol of isopropanol (Acros 99.5%). The addition of thissecond solution takes place dropwise at 0° C., with continued flushingwith argon. The various alcohols present are then removed by heating thereaction mixture at 80° C. for about 3 hours. Finally, 37 g ofdemineralized water are added so that the volume of the precursorsolution is equal to ⅔ of the volume of the autoclave in which thetitano-silicalite zeolite is then crystallized. The molar composition ofthe resulting clear solution is: SiO₂/TiO₂/TPAOH/H₂O=1/0.02/0.35/21.

Maturation of the Precursor

The precursor obtained is placed in a 250 mL autoclave and is thenheated at 80° C. and 30 bar, without stirring, for a given time of 14hours. The pressure is adjusted by means of an inert gas such asnitrogen.

Crystallization

The matured precursor is crystallized, without stirring, at 175° C. and60 bar, for 5 days. The pressure is adjusted by means of an inert gassuch as nitrogen.

Washing, Drying, Calcination

The material obtained after the crystallization step is recovered bycentrifugation for 30 to 45 minutes, at 9° C. and 12 000 rpm, and isthen washed, i.e. dispersed in about 150 to 200 mL of demineralizedwater and left stirring for about 1 hour. The washing operation isrepeated a sufficient number of times (in general three times) such thatthe pH of the final washing water is less than 9. Between each wash, thesolid is recovered by centrifugation for 30 to 45 minutes, at 9° C. and12 000 rpm. Next, the product is dried at 80° C. for about 16 hours andis then calcined at 550° C. in air for 3 hours.

Phenol Hydroxylation Reaction

The hydroxylation of phenol is performed in a one-liter semi-batchstirred reactor (500 rpm), to which are first added 200 g of phenol, 60g of solvent such as water, acetone or methanol and 6 g of catalyst(TS-1 or TS-2). The reactor is equipped with a jacket in whichcirculates a heat-exchange fluid heated to 85° C. to obtain atemperature of 80° C. in the reaction medium. The start of the reactioncorresponds to the start of introduction of the 69.5 g of hydrogenperoxide at 26% by weight in water. This solution is added dropwise over2 hours. After the end of addition of the aqueous hydrogen peroxidesolution, two or three samples of 5 to 10 g of the reaction medium arecollected. These samples make it possible both to determine theremaining amount of hydrogen peroxide by potentiometric assay, and alsoto quantify, by liquid-phase chromatographic analysis, the pyrocatechol(PC) and hydroquinone (HQ). Under these operating conditions, thephenol/H₂O₂/H₂O mole ratio is 1/0.25/2.9 and the phenol/TS-1 mass ratiois 1/0.03.

Assay of the Aqueous Hydrogen Peroxide Solution and of the PhenolConversion Products

The aqueous hydrogen peroxide solution is assayed by oxidation of iodideions and back-assay of the formed iodine with sodium thiosulfate. Thepotentiometric titration station used for this analysis is a Titrelab®865 from the company Radiometer Analytical.

Pyrocatechol and hydroquinone are analyzed by liquid-phasechromatography (Agilent 1200 series).

In the examples that follow, the following abbreviations have themeanings as follows:

The degree of conversion (DC(H₂O₂)) of hydrogen peroxide corresponds tothe ratio between the number of moles of hydrogen peroxide converted andthe number of moles of hydrogen peroxide introduced.

The diphenol reaction yield (RY(HQ+PC)/H₂O₂) corresponds to the ratiobetween the number of moles of diphenols formed(pyrocatechol+hydroquinone) and the number of moles of hydrogen peroxideintroduced.

The pyrocatechol reaction yield (RY(PC)/H₂O₂) corresponds to the ratiobetween the number of moles of pyrocatechol formed and the number ofmoles of hydrogen peroxide introduced.

The hydroquinone reaction yield (RY(HQ)/H₂O₂) corresponds to the ratiobetween the number of moles of hydroquinone formed and the number ofmoles of hydrogen peroxide introduced.

The diphenol selectivity (CY(HQ+PC)/H₂O₂) corresponds to the ratiobetween the number of moles of diphenols formed(pyrocatechol+hydroquinone) and the number of moles of hydrogen peroxideconverted.

Example 1 Effect of the Maturation Step on the Catalytic Performance ofTS-1 in the Phenol Hydroxylation Reaction

The phenol hydroxylation reaction described above was performed withzeolites obtained according to process C (examples 1.1 and 1.2),according to process A (example 1.3), according to process D (example1.4) and according to process B (example 1.5) in which the maturationstep is performed at 80° C. for 14 hours, the crystallization step at175° C. for 5 days, and the calcination step at 550° C. for 3 hours.Samples were collected from the reaction medium 15 and 60 minutes afterthe end of the addition of H₂O₂. The results are presented in table 1.

Comparative reactions were performed with zeolites obtained according toprocess C (example 1.6), process A (example 1.7) and process D (example1.8), but which did not undergo the maturation step. These zeolites onlyunderwent the step of crystallization at 175° C. for 5 days and the stepof calcination at 550° C. for 3 hours. Samples were collected from thereaction medium 15 and 60 minutes after the end of the addition of H₂O₂.The results are presented in table 2.

TABLE 1 Sample collection Examples according to the invention (T₀ = 2 h= 1.1 1.2 1.3 1.4 1.5 addition T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + T₀ +T₀ + T₀ + time of H₂O₂) 15 min 60 min 15 min 60 min 15 min 60 min 15 min60 min 15 min 60 min DC(H₂O₂) (%) 89 99 93 99 84 98 93 99 85 98RY(HQ)/H₂O₂ 49 53 46 46 43 46 49 49 40 49 (%) RY(PC)/H₂O₂ 30 32 29 28 2729 29 31 29 30 (%) RY(HQ + PC)/ 79 85 75 74 70 75 78 80 70 78 H₂O₂ (%)CY(HQ + PC)/ 89 86 81 75 83 76 83 80 82 79 H₂O₂ (%) PC/HQ 0.62 0.61 0.630.62 0.64 0.63 0.59 0.63 0.73 0.61 mole ratio

TABLE 2 Sample collection Comparative examples (T₀ = 2 h = 1.6 1.7 1.8addition time T₀ + 15 T₀ + 60 T₀ + 15 T₀ + 60 T₀ + 15 T₀ + 60 of H₂O₂)min min min min min min DC(H₂O₂) (%) 67 81 65 80 74 89 RY(HQ)/H₂O₂ (%)26 31 24 28 32 37 RY(PC)/H₂O₂ (%) 20 24 21 23 23 26 RY(HQ + PC)/ 46 5445 52 55 63 H₂O₂ (%) CY(HQ + PC)/ 69 67 69 65 74 71 H₂O₂ (%) PC/HQ moleratio 0.78 0.77 0.89 0.83 0.71 0.70

The results show that the catalytic performance of the materialscrystallized after the maturation step are markedly better than those ofthe materials crystallized without maturation. Specifically, from akinetic point of view, 15 minutes after the end of addition of theaqueous hydrogen peroxide solution (T₀+15 min), an H₂O₂ conversion of84% for a matured TS-1 prepared according to protocol A (example 1.3) isobserved, whereas it is only 65% for the material synthesized accordingto the same protocol but without the maturation step (example 1.7).Furthermore, for an equivalent conversion of hydrogen peroxide (about80%), this same material has a selectivity toward PC+HQ relative tohydrogen peroxide of 83% (example 1.3), whereas it is only 69% for itsnon-matured homolog (example 1.7). The same observations may be madewith all of the TS-1 products synthesized according to the otherprotocols. Furthermore, it is observed, independently of the syntheticprotocol, that a PC/HQ mole ratio close to 0.60 is obtained for the TS-1products matured for 14 hours at 80° C.

Example 2 Effect of the Maturation Step on the Structure of the TS-1

Zeolites were prepared according to process A (example 2.1), process D(example 2.2), process C (example 2.3) and process B (example 2.4) witha maturation step at 80° C. for 4.5 to 48 hours or without a maturationstep. All the zeolites prepared underwent a step of crystallization at175° C. for 5 days and a step of calcination at 550° C. for 3 hours.

The size of the crystallites was determined by X-ray diffraction (XRD)and transmission electron microscopy (TEM) after the maturation,crystallization and calcination steps. The size of the crystallites wasalso determined by dynamic light scattering (DLS) using syntheticaqueous solutions (i.e. solutions obtained after maturation, aftercrystallization and before calcination of the materials) diluted from 10to 400 times in demineralized water and/or treated with ultrasound for 1to 10 minutes, but also using solutions obtained after dispersion of 50to 100 mg of matured, crystallized and calcined catalyst in 10 g ofdemineralized water, and treated with ultrasound for 15 minutes. Theouter surface area and the inter-grain distance were determined byadsorption/desorption of nitrogen. The results are presented in table 3.

TABLE 3 DLS XRD Size after Size after Apparent maturation maturation,Nitrogen mean size and crystal- adsorption/ of the crystallizationlization Population desorption crystallites and before and (% of the TEMS_(outer) D_(inter-grain) Exam- Matu- (line 101) calcination calcinationnumber of Crystallite (m²/g) (nm) ples ration (nm) (nm) (nm)crystallites) size (nm) [tplot] [BJH] 2.1 None 80 — — — 90-160 39 50 ±20 4.5 h/ 67 71 71 94 50-110 63 22 ± 7  80° C. 14 h/ 55 — 59 97 30-90 79 19 ± 5  80° C. 23 h/ 56 56 54 97 30-90  83 16 ± 6  80° C. 48 h/ 55 5151 98 40-90  82 21 ± 7  80° C. 2.2 None 95 — — — — 33 40 ± 15 14 h/ 50 —— — — 72 19 ± 5  80° C. 2.3 None 110  — — — — 22 60 ± 20 14 h/ 68 — — —— 60 30 ± 10 80° C. 2.4 14 h/ 55 — — — — 79 19 ± 6  80° C.

The main characteristic of the materials matured at 80° C. is that theapparent mean size of the particles is about 1.5 to 2 times smaller thanthat of the non-matured materials (size determined after OLS analysis,observation by TEM and calculated after XRD analysis from the mid-heightwidth of the line (101)). Furthermore, irrespective of the syntheticprotocol, it is observed that TS-1 particles of 50 to 70 nm are obtainedif the zeolite has undergone a maturation step, irrespective of thematuration time at 80° C. Since the particles are smaller aftermaturation, the space between the grains (D_(inter-grain) determined viathe BJH method) is consequently smaller. Furthermore, the zeolitesmatured for 4.5 to 48 hours at 80° C. have an outer surface area abouttwice as large as that of the non-matured materials. From the DLS,irrespective of the synthetic protocol and the maturation time at 80°C., the size of the crystallites obtained after the maturation andcrystallization steps and before the calcination step is similar, oreven identical, to the size of the crystallites obtained after thematuration, crystallization and calcination steps.

Example 3 Effect of the Maturation Time and Temperature on the CatalyticPerformance of TS-1 in the Phenol Hydroxylation Reaction

The hydroxylation reaction presented above was performed with differentzeolites prepared according to protocol A which have undergone amaturation step at 80° C. for 4.5 hours (example 3.2), for 14 hours(example 3.3), for 23 hours (example 3.4) and for 48 hours (example 3.5)and at 90° C. for 14 hours (example 3.6) and for 23 hours (example 3.7).

A comparative example (example 3.1) of hydroxylation of phenol was alsoperformed with a zeolite obtained via process A, but which was notsubjected to the maturation step.

All the zeolites prepared underwent a step of crystallization at 175° C.for 5 days and a step of calcination at 550° C. for 3 hours.

Samples were collected from the reaction medium 15 and 60 minutes afterthe end of the addition of H₂O₂. The results are presented in table 4.

TABLE 4 Examples Sample 3.1 3.2 3.3 3.4 3.5 3.6 3.7 collectionMaturation (T₀ = 2 h = 4.5 h/ 14 h/ 23 h/ 48 h/ 14 h/ 23 h/ additionNone 80° C. 80° C. 80° C. 80° C. 90° C. 90° C. time of T₀ + T₀ + T₀ +T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + T₀ + H₂O₂) 15 min 60min 15 min 60 min 15 min 60 min 15 min 60 min 15 min 60 min 15 min 60min 15 min 60 min DC(H₂O₂) 65 80 80 94 84 98 93 99 65 82 78 95 83 98 (%)RY(HQ)/ 24 28 32 40 43 46 47 49 28 34 36 41 36 37 H₂O₂ (%) RY(PC)/ 21 2323 28 27 29 29 30 20 24 24 27 24 24 H₂O₂ (%) RY(HQ + 45 52 55 68 70 7577 78 48 58 60 68 59 61 PC)/ H₂O₂ (%) CY(HQ + 69 65 69 72 83 76 83 79 7471 77 72 71 63 PC)/ H₂O₂ (%) PC/HQ 0.89 0.83 0.69 0.69 0.64 0.63 0.620.60 0.71 0.69 0.68 0.65 0.66 0.65 mole ratio

It is noted that it is possible to vary the selectivity towardhydroquinone and pyrocatechol relative to hydrogen peroxide(CY(HQ+PC)/H₂O₂) which ranges between 60% and 85% by modifying thematuration temperature of between 80 and 90° C. and the maturation timeof between 4.5 and 48 hours. On the other hand, irrespective of thematured catalysts, the PC/HQ mole ratios are similar or even identicaland strictly less than 0.70.

Example 4 Effect of the Crystallization Time on the CatalyticPerformance of Matured TS-1 in the Phenol Hydroxylation Reaction

The hydroxylation reaction presented above was performed with differentzeolites prepared according to protocol A which have undergone a step ofmaturation at 80° C. for 14 hours and a step of crystallization at 175°C. for 6 hours (example 4.1), for 24 hours (example 4.2) and for 5 days(example 4.3). All the zeolites were calcined at 550° C. for 3 hours.

Samples were collected from the reaction medium 15 and 60 minutes afterthe end of the addition of H₂O₂. The results are presented in table 5.

TABLE 5 Examples 4.1 4.2 4.3 Crystallization Sample collection 6 h/175°C. 24 h/175° C. 5 days/175° C. (T₀ = 2 h = T₀ + T₀ + T₀ + T₀ + T₀ + T₀ +addition time of 15 60 15 60 15 60 H₂O₂) min min min min min minDC(H₂O₂) (%) 84 98 95 99 84 98 RY(HQ)/H₂O₂ (%) 43 46 44 48 43 46RY(PC)/H₂O₂ (%) 27 28 28 29 27 29 RY(HQ + PC)/ 70 74 72 77 70 75 H₂O₂(%) CY(HQ + PC)/ 84 75 76 78 83 76 H₂O₂ (%) PC/HQ mole ratio 0.64 0.610.62 0.61 0.64 0.63

The results show that after maturation for 14 hours at 80° C., thecrystallization time at 175° C. may be lowered to 6 hours withoutmodifying the catalytic performance of the TS-1. Specifically, atvirtually total conversion of the hydrogen peroxide, the CY(HQ+PC)/H₂O₂values are very similar and, respectively, 75%, 78% and 76% forcrystallizations times at 175° C. of 6 hours, 24 hours and 5 days.Finally, irrespective of the crystallization time at 175° C., the PC/HQmole ratio is 0.60.

Example 5 Effect of the Crystallization Time on the Characteristics ofthe TS-1

Different zeolites prepared according to protocol A underwent a step ofmaturation at 80° C. for 14 hours and a step of crystallization at 175°C. for 6 hours (example 5.1), for 24 hours (example 5.2) and for 5 days(example 5.3). All the zeolites were calcined at 550° C. for 3 hours.

The size of the crystallites was determined by XRD and DLS. The resultsare presented in table 6.

TABLE 6 XRD Apparent DLS mean size Population Ti/ of the (% of the (Ti +Si) crystallites number of molar (line 101) Size crystal- ExamplesCrystallization (±0.001) (nm) (nm) lites) 5.1  6 h/175° C. 0.013 49 — —5.2 24 h/175° C. 0.016 53 54 93 5.3 5 days/175° C.  0.020 55 59 97

The results show that the size of the crystallites, of about 50 nm, doesnot depend on the crystallization time at 175° C. for materials maturedbeforehand for 14 hours at 80° C. On the other hand, it is observed thatthe titanium content of the material increases as the crystallizationtime increases. The mole ratio Ti/(Ti+Si) is, respectively, 0.013, 0.016and 0.020 for crystallization times at 175° C. of 6 hours, 24 hours and5 days. The increase in titanium content of 0.013 to 0.016 and 0.020corresponds to the increasingly large formation of anatase, as evidencedin FIG. 8.

Example 6 Effect of the Nature of the Solvent in the PhenolHydroxylation Reaction in the Presence of a Catalyst of thetitano-silicalite Zeolite Type

The hydroxylation reaction presented above was performed with differentsolvents or a mixture of solvents such as water (example 6.1),water/acetone (example 6.2) and water/methanol (example 6.3).

The zeolite used for the phenol hydroxylation reaction was preparedaccording to protocol A and was first subjected to a step of maturationat 80° C. for 23 hours, and then a step of crystallization at 175° C.for 5 days, and finally a step of calcination at 550° C. for 3 hours.

Samples were collected from the reaction medium 15, 60 or 120 minutesafter the end of the addition of H₂O₂. The results are presented in thetable below.

Examples 6.1 6.2 6.3 Sample collection Solvent (T₀ = 2 h = WaterWater/acetone Water/methanol addition time of T₀ + T₀ + T₀ + T₀ + T₀ +T₀ + T₀ + T₀ + H₂O₂) 15 min 60 min 15 min 60 min 120 min 15 min 60 min120 min DC(H₂O₂) (%) 93 99 67 84 97 70 90 98 RY(HQ)/H₂O₂ (%) 47 49 27 3235 32 36 37 RY(PC)/H₂O₂ (%) 29 30 26 30 33 22 25 25 RY(HQ + PC)/ 77 7852 62 68 54 60 62 H₂O₂ (%) CY(HQ + PC)/ 83 79 79 74 70 77 67 63 H₂O₂ (%)PC/HQ mole ratio 0.62 0.60 0.96 0.95 0.94 0.69 0.69 0.69

The results show that the best solvent for the hydroxylation of phenolis water used alone. Specifically, from a kinetic point of view, 60minutes after the end of addition of the hydrogen peroxide (T₀+60 min),a total conversion of the hydrogen peroxide is observed for thehydroxylation of phenol in water, whereas it is only 84% and 90% for thehydroxylation of phenol, respectively, in water/acetone andwater/methanol. Furthermore, for an equivalent conversion of hydrogenperoxide (about 100%), the hydroxylation of phenol in water leads to aselectivity toward PC+HQ relative to the hydrogen peroxide of 79%, whichis higher than that obtained for the hydroxylation of phenol in thewater/acetone and water/methanol mixtures, which are, respectively, 70%and 63%. Finally, the lower PC/HQ ratio was obtained for thehydroxylation of phenol in water (PC/HQ=0.60). This is, respectively,0.94 and 0.69 for the hydroxylation of phenol in the water/acetone andwater/methanol solvent mixtures.

1.-11. (canceled)
 12. A matured TS-1 or TS-2 titano-silicalite zeolitehaving: an apparent mean particle size of from 35 to 75 nm, an outersurface area of from 60 m²/g to 150 m²/g, and an inter-grain distance offrom 10 to 30 nm. 13.-14. (canceled)
 15. The matured TS-1 or TS-2titano-silicalite zeolite according to claim 12 further having aspecific surface area of between 350 and 600 m²/g.
 16. The matured TS-1or TS-2 titano-silicalite zeolite according to claim 12 further having aspecific surface area of between 400 and 500 m²/g.
 17. The matured TS-1or TS-2 titano-silicalite zeolite according to claim 12 further havingmicropores of between 0.40 and 0.50 nm.
 18. The matured TS-1 or TS-2titano-silicalite zeolite according to claim 12 further havingmicropores of between 0.44 and 0.46 nm.
 19. The matured TS-1 or TS-2titano-silicalite zeolite according to claim 12 further having a moleratio Ti/(Ti+Si) of from 0.0001 to 0.10.
 20. A process for preparing aTS-1 or TS-2 titano-silicalite zeolite, comprising the following steps:a) preparation of a zeolite precursor from at least one source ofsilicon, at least one source of titanium, at least one mineralizingagent and at least one structuring agent; b) maturation of the zeoliteprecursor for obtaining a matured precursor; c) crystallization of thematured precursor for obtaining a matured crystalline precursor, andoptionally d) calcination of the matured crystalline precursor, whereinsaid maturation step consists in a step of thermal heating of saidzeolite precursor, before crystallization, at a temperature of from 70to 100° C.
 21. The process according to claim 20, wherein saidmaturation step consists in a step of thermal heating of said zeoliteprecursor, before crystallization, at a temperature of 80° C. or 90° C.22. The process according to claim 20, wherein the maturation step isperformed for a time of from 30 minutes to 9 months.
 23. The processaccording to claim 20, wherein the maturation step is performed for atime of from 1 hour and 15 days.
 24. The process according to claim 20,wherein the source of titanium is a titanium alkoxide.
 25. The processaccording to claim 20, wherein the source of silicon is a siliconalkoxide.
 26. A TS-1 or TS-2 titano-silicalite zeolite that may beobtained by the process according to claim
 20. 27. A method forhydroxylating an aromatic compound, wherein said aromatic compound isreacted with an oxidizing agent in the presence of a catalyst, saidcatalyst being a TS-1 or TS-2 titano-silicalite zeolite according toclaim
 12. 28. A method for hydroxylating an aromatic compound, whereinsaid aromatic compound is reacted with an oxidizing agent in thepresence of a catalyst, said catalyst being a TS-1 or TS-2titano-silicalite zeolite according to claim 15.